1. Field of the Invention
The present general inventive concept relates to a digital audio amplifier, and more particularly, to a digital audio signal amplifier in which both safety and power efficiency are achieved by integrating a switching mode power supply and a digital audio amplifier into one body, and a digital audio signal amplifying method thereof.
2. Description of the Related Art
In general, a digital audio system includes a direct current (DC) voltage supply unit generating a DC voltage from a commercial alternating current (AC) voltage; and a digital audio amplifier pulse-modulating the DC voltage using an audio signal, low-pass filtering the pulse-modulated DC voltage, and obtaining an output audio signal corresponding to the input audio signal.
Here, for the safety of users, the DC voltage supply unit is required to have a function of insulating the commercial AC voltage from the digital audio amplifier. Accordingly, a switching mode power supply (SMPS) having an insulation transformer is generally used as the DC voltage supply unit. Meanwhile, the digital audio amplifier is generally a D class digital audio amplifier to increase the output power.
FIG. 1 is a block diagram illustrating a conventional digital audio system 100. The audio system 100 of FIG. 1 includes an SMPS 110 and a D class audio amplifier 130.
The SMPS 110 converts an input commercial AC voltage into a DC voltage using a first rectifying and smoothing unit 112, switches the DC voltage in a switching unit 116 operating at a rate corresponding to a pulse width modulation (PWM) signal having a frequency of tens to hundreds of kHz or higher generated in a PWM modulation unit 114, transforms the switched DC voltage with an insulation transformer 118 having an appropriate winding ratio, rectifies the output of the insulation transformer 118 through a second rectifying and smoothing unit 120, and outputs a DC voltage. Also, though it is not shown, an error signal is fed back to the PWM modulation unit 114 to adjust a frequency of a pulse modulated signal and a duty ratio, so that a constant DC voltage can be output irrespective of changes in the input voltage or output current.
The insulation transformer 118 insulates a primary coil side, i.e., the commercial AC voltage source, from a secondary coil side, i.e., the digital audio amplifier 130. Also, an error signal detected in the secondary side is fed back to the PWM modulation unit 114 of the primary side through a photo coupler (not shown) to provide electrical isolation.
Meanwhile, the D class digital audio amplifier 130 switches the DC voltage provided by the SMPS 110 at a D class output end 134 by a PWM audio signal generated from the PWM modulation unit 132, low-pass filters the switched DC voltage through a low-pass filter 136, and generates an output audio signal corresponding to an original audio signal. Meanwhile, though it is not shown, in order to stabilize the audio output a negative feedback signal is generated from the output of the insulation transformer 118 to control the pulse modulation of the PWM modulation unit 114.
FIG. 2 illustrates waveform diagrams illustrating an operation of the D class digital audio amplifier 130 of FIG. 1. Referring to FIG. 2, a PWM audio signal is obtained by modulating a 180 kHz or higher triangular wave carrier with an input audio signal of 20 kHz or lower. The switched DC voltage is obtained by switching the DC voltage with the PWM audio signal. Also, the output audio signal is obtained by low-pass filtering the switched DC voltage. As illustrated in FIG. 2, the input audio signal is similar to the output audio signal.
However, the conventional digital audio system as illustrated in FIG. 1 has a problem in that the power efficiency is low and the manufacturing cost is high.
For example, assuming that the power efficiency of the SMPS 110 is P1 and the power efficiency of the digital audio amplifier 130 is P2, the power efficiency Pt of a conventional digital audio system 100 is P1×P2. Here, since each of P1 and P2 has a value less than 1, and Pt becomes less than P1 and P2, respectively, the conventional digital audio system 100 has very low power efficiency.
Meanwhile, in the SMPS 110 and the digital audio amplifier 130 of FIG. 1, the PWM modulation units 114 and 132 perform the same PWM modulation, the rectifying and smoothing units 112 and 120 perform the same rectifications, and the switching unit 116 and the D class output end 134 perform the same switching operation. That is, it can be seen that the units performing the same operation are disposed redundantly, accordingly manufacturing costs are increased.